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Novel perfluorinated dienes

Abstract

The research described within this thesis may be divided into four areas: 1) Unsaturated perfluorinated systems have been reduced, or defluorinated, using alkali metal amalgams to give products with a higher degree of unsaturation. For example, perfluoro-3,4-dimethylhex-3-ene (105) can be reduced to perfluoro-3,4- dimethylhex-2,4-diene (106). Remarkably, these reductions have also been performed, with equal success, using an electron rich amine, tetrakis(dimethylamino)ethene (107), which avoids the difficult, and potentially hazardous, use of amalgams. A difluoride salt, of amine (107), is produced as a by-product, which has potential as a soluble fluoride ion source.2) Diene (105) is highly electron deficient and, therefore, is susceptible to nucleophilic attack, which occurs at the vinylic positions. This compound was reacted with difunctional oxygen nucleophiles, forming potential polymer precursors, which remain reactive towards nucleophiles, suggesting the possibility of their use in block co-polymer syntheses to give highly fluorinated products.3) Calcium hypochlorite has been utilised to oxidise perfluorinated alkenes and dienes to yield the corresponding epoxide(s). An alternative methodology, using t-butyl hydroperoxide and butyl lithium, has been successfully applied to perfluorinated systems, for the first time, to give previously inaccessible compounds. The diepoxide (162) has been shown to undergo an unusual thermal ring opening, and expansion, to form a perfluorinated dioxin (179).4) An efficient route to hexakis(trifluoromethyl)cyclopentadiene (181) has been developed via an unusual cyclisation process, which is induced by fluoride ion. This diene displays an interesting chemistry, including its reduction by tetraalkylammonium iodides to form the pentakis(trifluoromethyl)cyclopentadienyl anion, as crystalline ammonium salts (tetraethyl show below), in good yields. When these salts are combined with concentrated sulphuric acid, 5H-pentakis(trifluoromethyl)cyclopentadiene (188) is produced, which is the strongest non-conjugated carbon acid known.